Remove bazel status from build documentation
Remove bazel status from build documentation

The main audience of this page is developers who want instructions for
building Gerrit.  When there were two build systems, the description
of what works and what doesn't here was useful for such developers to
decide which system to use.

Remove the feature overview to make this page easier to read.

Now that bazel is the only build system, missing features that people
were relying on should be filed in the bug tracker instead.

Change-Id: Idd34fe8c6fe628735f1a36c6803959850cc4a1dd

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